Conversion of hydrocarbons



Patented July 26, 1938 UNITED STATES CONVERSION OF HYDROCARBONS IJacqueC. Morrell and Arlstid V. Grosse, Chicago, Ill., assignors toUniversal Oil Products Company, Chicago, Ill., a corporation of DelawareNo Drawing. Application September 30, 1936, Serial No. 103,394

4 Claims. (Cl. 260-868) This. invention relates particularly to theconversion of straight chain hydrocarbons into closed chain or cyclichydrocarbons.

More specifically it is concerned with a process involving the use ofspecial catalysts and specific conditions of operation in regard totemperature, pressure and time of reaction whereby aliphatichydrocarbons can be efllciently converted int aromatic hydrocarbons.

In the straight pyrolysis of pure hydrocarbons or hydrocarbon mixturessuch as those encountered in fractions from petroleum or other naturallyoccurring or synthetically produced hydrocarbon mixtures the reactionsinvolved which produce aromatics from parafiins and olefins are of anexceedingly complicated-character and cannot be very readily controlled.I

It is generally recognized that, in the thermal decomposition ofhydrocarbon compounds or hydrocarbon mixtures of relatively narrow rangethat whatever intermediate reactions are involved,

there is an overall loss of hydrogen, a tendency tocarbon separation anda generally wider severity using higher temperatures and higher times ofexposure to pyrolytic conditions, there is a progressive increase inloss of hydrogen and a large amount of secondary reactions involvingrecombination of primary radicals to form polymers and some cyclizationto form naphthenes and aromatics, but the mechanisms involved in thesecases are of so complicated a nature that very little positiveinformation has been evolved in spite of the large amount ofexperimentation which has been done and the large. number of theoriesproposed. In general, however, it may be said that starting withparafiin hydrocarbons representing the highest degree' of saturationthat these compounds are changed progressively into olefins, naphthenes,aromatics, and finally into carbon andhydrogen and other light fixedgases. It is not intended to infer from this statement that anyparticular success has attended the conversion of any given paraflin orother aliphatic As the conditions of pyrolysis are increased inhydrocarbon into an aromatic hydrocarbon ofthe same number of carbonatoms by way-of the progresive steps shown. If this is done it isusually with very low yields which are of very little practicalsignificance.

The search for catalysts to specifically control and accelerate desiredconversion reactions among hydrocarbons has been attended with the usualdifllculties encountered in finding catalysts for other types ofreactions since there are no basic laws or rules for predicting theeffectiveness of catalytic materials and the art as a whole is in amoreor less empirical state. In using catalysts even in connection withconversion reactions among pure hydrocarbons and particularly inconnection with the conversion of the relatively heavy distillates andresidua which are available for cracking, there is a general tendencyfor the decomposition reactions to proceed at a very rapid rate,necessitating the use of extremely short time factors and very accuratecontrol of REISSUEU.

temperature and pressure to avoid too extensive decomposition. There arefurther difilculties encountered in maintaining the efiiciency ofcatalysts employed in pyrolysis since there is usually a rapiddeposition of carbonaceous materials on their surfaces and in theirpores.

The foregoing brief review of the art of hydrocarbon pyrolysis is givento furnish a general background for indicating the improvement in suchprocesses which is embodied in the present invention, which may beapplied to the treatment of pure paraflin or olefin hydrocarbons,hydrocarbon mixtures containing-substantial percentages of parafiinhydrocarbons such as relatively close out fractions producible bydistilling petroleum, and analogous'fractions which contain unsaturatedas well as saturated straight chain hydrocarbons, such fractionsresulting from cracking operations upon the heavier fractions ofpetroleum.

In one specific embodiment the present invention comprises theconversion of aliphatic hydrocarbons including parafiln and olefinhydrocarbons into aromatic hydrocarbons by subjecting them at elevatedtemperatures of the order of 400-700 C. to contact for definite, timesof the order of- 6--'50 seconds with catalytic materials comprisingmajor proportions of refractory carri'ers of relatively low catalyticactivity supportingminor proportions of compounds of elements selectedfrom those occurring in the lefthand column of Group V of the periodictable, these compounds having relatively high catalytic activity.

According to the present invention aliphatic or straight chainhydrocarbons having 6 or more carbon atoms .in chain arrangement in.their structure are specifically dehydrogenated in such a way that thechain of carbon atoms undergoes ring closure with the production in thesimplest case of benzene from n-hexane or nehexene and in the case ofhighermolecular weight paraffins of various alkyl derivatives ofbenzene. Under properly controlled conditions of times of contact,temperature and pressure very high yields of the order of '75- to 90% ofthe benzene or aromatic compounds are obtainable which are far in excessof any previously obtained in the art either with or without catalysts.For the sake of illustrating and exemplifying the types of hydrocarbonconversion reactions which are specifically accelerated under thepreferred conditions by the present types of catalysts, the following.structural equations are introduced. Y

In the foregoing table the structural formulas of the primary paraffinhydrocarbons have been represented as a nearly closed ring instead bf bythe usual linear arrangement for the sake of indicating the possiblemechanisms involved. No attempt has been made to indicate the possibleintermediate existence of m'ono-olefins, diolefins, hexamethylenes oralkylated hexamethylenes which might result from the loss of variousamounts of hydrogen. It is not known at the "present time whether ringclosure occurs at the loss of onehydrogen molecule or whether dehy-,

drogenation of the chain carbons occurs so that the first ring compoundformed is an aromatic such as benzene or one of its derivatives. Theabove three equations are of a relatively simple character indicatinggenerally the type of reactions involved but in the case ofn-parafllnsor mono-olefins of higher molecular weight than the octane shown and inthe case of branch chain compounds which contain various alkylsubstituent groups in different positions along the six-carbon atomchain, more complicated reactions will be involved. For example, in thecase of such a primary compound as 2,3-dimethyl hexane the principalresultant productis apparently o-xylene although'there are concurrentlypro,- duced definite yields of such compounds as ethyl benzeneindicating an isomerization of two substituent methyl groups. In thecase of no'nanes which are represented by the compound 2,3,4-trimethylhexane, there is formation not only of mesitylene but also of suchcompounds as methyl ethyl benzol and various propyl benzols.

It will be seen from theforegoing that the scope of the presentinventionis preferably limited to the treatment of aliphatic hydrocarbons which,contain at least 6 carbon atoms in straight chain arrangement. In thecase of paraflin hydrocarbons containing less than 6 carbon atoms inlinear arrangement, some formation of aromatics may take place due toprimary isomerization reactions although obviously the extent of thesewill vary considerably with the type of compound and the conditions ofoperation. The process is readily applicable to paraffins from hexane upto dodecane'and their corresponding With increase in molecular weightbeyond this point the percentage of undesirable side reactions tends toincrease and yields of the desired alkylated aromatics decrease inproportion.

'Thepresent invention is characterized by the use of a particular groupof composite catalytic materials which employ as their base catalystsare put in regard to temperature during service and in regeneration bymeans. of air or other oxidizing gas mixtures after they have becomefouled with carbonaceous deposits after a period of service. As examplesof materials which may be employed in granular form as supports for thepreferred catalytic substances may be men tioned the following:

Magnesium oxide Montmorillonite clays Aluminum oxide Kieselguhr BauxiteCrushed iirebrick Bentonite clays Crushed silica Glauconite (greensand)It should be emphasized that in the field of catalysis there have beenvery few rules evolved which will enable the prediction of whatmaterials will catalyze a given reaction. Most of the catalytic work hasbeen done on a purely empirical basis, even though at times certaingroups of elements or compounds have been found to be more or lessequivalent in accelerating certain oxide may be replaced to the extentof several percent by ferrous oxide. The mineral is of quite commonoccurrence and readily obtainable in quantity at a reasonable figure.

at a temperature of 350 0., though the rate of decomposition onlyreaches a practical value at considerably higher temperatures, usuallyof the order of 800 C. to 900 C. Magnesite is related The pure,.compound begins to decompose to form the oxide chemical methods may beused alternatively in place of the natural mineral, as a more reactiveconstituent of carriers consisting of spacing materials of relativelyinert character and in some cases allowing the production of catalystsof higher efliciency and longer life. It is not necessary that themagnesite be completely converted to oxide but as a rule it ispreferable that the conversion be at least over 90%, that is, so thatthere is less than 10% of the carbonate remaining in the ignitedmaterial.

Aluminum oxide which is generally preferable as a base material for themanufacture of catalysts for the process may be obtained from naturalaluminum oxide minerals or ores such as bauxite or carbonates such asdawsonite by proper calcination, or it may be prepared by precipitationof aluminum hydrate from solutions of aluminum sulfate or differentalums, and dehydration of the precipitate of aluminum hydroxide by heat,and usually it is desirable and advantageous to furthertreat it with airor other gases, or by other means to activate it prior to Two hydratedoxides or aluminum occur in nature, to-wit, bauxite having I the formulaA12O3.2H2O and diaspore Al203.HzO.- In both of these oxides ironsesqui-oxide may, partially replace the alumina- These two minerals orcorresponding oxides produced. from precipitated aluminum. hydroxide areparticularly suitable for the manufacture of thepresent type ofcatalysts andin some instances have given the best resuits of any of thebase compounds whose use is at present contemplated. The mineraldawsonite having the formula NasA1(COa)3.2Al(OH)3 is another mineralwhich may be used as a source of aluminum oxide;

It is best practice in the final steps of preparing aluminum oxide as abase catalyst to ignite for some time at temperatures within the sameapproximate range as those employed in the ignition of magnesite,;to-wit, from 800-900 C. This probably does not correspond to completedehydration of the hydroxides but apparentlygives a catalytic materialof good strength and porosity so that it is able to resist for a longperiod of time the deteriorating effects of the service and regenerationperiods to which it is subjected. In the case of the clays which mayserve as base catalytic. materials for supporting promoters, the bettermaterials-are those which have been acid-treated to render them moresiliceous. These may be pelleted or formed in any. manner before orafter the addition of the promoter-catalyst since ordinarily they have ahigh percentage of fines. 'The addition of certain of the promoters,however, exerts a binding influence so that the-formed materials may beemployed without fear of in service. 1 I

4 Our investigations have also definitely demonstrated that thecatalytic emciency of such substructural deterioration compounds andmore particularly oxides of the elements in the lefthand column. ofGroup V of the periodic table including vanadium, columbium andtantalum. In general practically all of the compounds of the preferredelements will have some catalytic activity though as a rule the oxidesandparticularly the lower oxides are the best catalysts.

elements in aqueous solutions from which they are absorbed by preparedgranular carriers or from which they are deposited upon the carriers byevaporation of the solvent. The invention furthercomprises the use ofcatalyst composites madeby mixing relatively insoluble compoundsCatalyst composites may be preparedby utilizing the soluble compounds ofthe j with carriers either in the wet or the dry condition. In thefollowing paragraphs some of the compounds of the elements listed aboveare given which aresoluble in water and which may be used to addcatalytic material to carriers. The known oxides of these elements arealso listed.

Vanadium Catalysts comprising 2 to 5 percent by weight of the lower.oxides of vanadium such as the sesquioxide V203 and the .tetroxide V204may be used. Some of the monoxide V0 may be present in some instances.The oxides mentioned are particularly eflicient as catalysts for thepresent types of reactions but the invention not limited to their usebut may employ other co pounds of vanadium. Thus solutions of theammonium and the alkali metal vanadates may be employed to add vanadiumcompounds to the carriers and also the soluble vanadylsulfates and thevanadium nitrate and carbonate. The alkaline earth vanadates may bemixed mechanically and also the halides of vanadium. The oxides per'seor those produced by reduction or decomposition of other vanadiumcompounds are preferred.

columbium A properly prepared carrier may be ground and sized to producegranules of relatively small mesh of the approximate order of from 4 to20 and these caused to absorb compounds which will ultimately yieldcompounds of columbium on heating to a proper temperature by' stirringthem with warm aqueous solutions-of soluble columbium compounds, such asfor example the mixed fluoride of columbium and potassium alreadymentioned having the formula CbOF2.2KF.H 2O, which q is sufficientlysoluble inwater to render is utilizable as a source of columbiumcatalyst. Other soluble compounds which may be used tov form catalyticdeposits containing columbium are the various alkali metal'columbates.Still other compounds of columbic acids, including salts of the alkalineearth and heavy metals, may be distributed upon the carriers bymechanical mixing either in the wet or the dry condition. As a rule thelower oxides are the best catalysts. The oxide resulting fromthedecomposition of such compounds as the pentahydroxide is for the mostpart the pentoxide CbzOt. I is reduced to a definite extent by hydrogenor by the gases and vaporous products resulting from the decompositionof the hydrocarbons treated in the-first stages of the process, so thatthe essen- This oxide, however,

tial catalysts for the larger portion of the period of service areevidently the lower oxides CbOz, Cb203, and CbO.

Tantalum Compounds of tantalum, such as for example. I

the pentoxide Tazos-and the tetroxide Ia-r04, and possibly thesesquioxide Tazoa, which result from the reduction of the pentoxide areparticularly efficient as catalysts for the present types of reactionsbut the invention is not limited to their use but may employ any of thecatalytically active compounds of tantalum. Tantalum fluoride and thedouble fluoride of tantalum and potassium having the formula TaKzFv aresoluble in water and may be conveniently used in aqueous solution asultimate sources of the oxides, which result from the ignition of theprecipitated hy-' droxide to form the pentoxide and the partialreduction of this oxide by hydrogen or the gases and Vapors in contactwith the catalyst in the.

normal operation of the process. The tantalum pentahydroxide may beprecipitated from a solution of the double fluoride by the use ofammonium or alkali metal hydroxides or carbonates as precipitants, thehydrate being later ignited to form the pentoxide, which may undergosome reduction as already stated.

The most general method for adding promoting materials to' the preferredbase catalysts, which if properly prepared have a high adsorptivecapacity, is to stir the preparedgranules of from approximately 4 to 20mesh into solutions ofsalts which will yield-the desired promotingcompounds on ignition under suitable conditions. In some] instances thegranules may be merely stirred in slightly warm solutions of salts untilthe dissolved compounds have been retained on the particles byabsorption-or occlusion, after'which the-particles are separated fromthe excess solvent by settling or filtration, washed with water toremove excess solution, and then ignited to produce the desired residualpromoter. In cases of certain compounds of relatively low solubility itmay be necessary to add the solutionin successive portions to theadsorbent bas'e catalyst with intermediate heating to drive off solventin order to 'get the required quantity of promoter deposited upon thesurface and in the pores ofthe base catalyst. The temperatures usedfor-drying and calcining after the addition of the promoters fromsolutions willdepend entirely upon the individual characteristics of thecompound added. and no general ranges of temperature can be given forthis step.

In some instances promoters may be deposited from solution by thevaddition of precipitants which cause the deposition of precipitates uponthe catalyst granules. As a rule methods of me chanical mixing are notpreferable, though in some instances in the case of hydrated or readilyfusible compounds these may be mixed with the proper proportions of basecatalysts and uniformly distributed during the'condition of fusing orfluxing.

In regard to the relative proportions of base fectiveness are obtainableby the deposition of as low as 1% or 2% of a. promoting compound uponthe surface and in the pores of the base catalyst,

. though the general average is about 5%. p

It has been found essential to the production of high yields ofaromatics from aliphatic hydrocarbons when using the preferred types ofcat-- alysts that depending upon the aliphatic hydrocarbon or mixture ofhydrocarbons being treated, temperatures from 400-'700 0. should beemployed, contact times of approximately 6 to 50 seconds and pressuresapproximately atmospheric. The use of subatmospheric pressures of theorder of A, atmosphere may be beneficial in that reduced .pressuresgenerally favor selective dehydrogenation reactions but on the otherhand moderately superatmospheric pressures usually of the order of lessthan 100 j lbs. per sq. in. tend to'increase the capacity of commercialplant equipment so that in practice a balance is struck between thesetwo factors.-

The times of contactmost commonly employed having from 6l2 carbon atomsto the molecule are of the orderfof 620 secs. It will be appreciated bythose familiar with the art of hydrocar bon conversion in the presenceof catalysts that "with n-paraflinic or mono-olefinic hydrocarbons thefactors of temperature, pressure and time will frequently have to beadjusted from the results of preliminary experiments to produce the bestresults in any given instance. The criterion of the yield of aromaticswillserve to fix the best conditions of operation. In a general sensethe relations between time, temperature and pressure are preferablyadjusted so that rather intensiveconditions are employed of sufficientsverltyto insure a maximum amount of the desired cyclization reactionswith a minimum of undesirable side reactions. If too. short times ofcontact are employed the conversion reactions will not proceed beyondthose of simple dehydrogenation and the yields of olefins and 'dioleflnswill predominate over those of aromatics.

While the present" process is particularly ap-' plicable tothe-production of the corresponding aromatics from an aliphatichydrocarbon or a' mixture of aliphatic hydrocarbons, the invention mayalso be, employed to produce aromatics from aliphatic hydrocarbonmixtures such'as distillates from p'araflinic or mixed base crudepetroleum. In this case the aromatic character offthe distillates willhave increased and as a rule the octane number will be higher. 'Ifdesired and found feasible on a basis of concentration, the aromaticsproduced in the hydrocarbon mixture may be recovered as such bydistillation into fractions of proper boiling range followed by chemicaltreatment with reagents capable of reacting selectively with them.Another method of aromatic concentration'will involve the use ofselective solvents. such as liquid sulfur dioxide, alcohols, furfural,chlorex, etc.

In operating the process the general procedure is to vaporizehydrocarbons or mixtures of hydrocarbons and after heating the vapors toa suitable temperature within the ranges previously specified, to passthem through stationary masses of granular catalytic material invertical cylindrical treating columns or banks of catalyst-' containingtubes in parallel connection. Since the reactions are endothermic it maybe necessary to apply some heat externally to maintain the best reactiontemperature. After passing through the catalytic zone the products aresubmitted to frac-' tionation to recover cuts or fractions containing 7I parts by weight of ammonium metavanadate in the desired aromaticproduct with the separation' of fixed gases, unconverted hydrocarbonsand heavier residual materials, which may be disposed of in any suitablemanner depending upon their composition. The overall yield of. aromaticsmay be increased by recycling the unconverted straight chainhydrocarbons to further treatment with .fresh material, although this isa more or less obvious expedient and not specifically characteristic ofthe present invention.

It is an important feature of the present process that the vaporsundergoing dehydrogenation should be free from all but traces of watervapor since the presence of any substantial amounts of steam reduces thecatalytic selectivity of the composite catalysts to a marked degree. Inview of the empirical state of the catalytic art, it is not intended tosubmit a complete explanation of the reasons for the deleteriousinfluence of water vapor on the course of the present type of catalyzedreactions, but it may be suggested that the action of the steam is tocause a partial hydration of such basic carriers as alumina andmagnesium oxide and some of the active'catalytic compounds due topreferential adsorption so that in effect the hydrocarbons are preventedfrom reaching or being adsorbed by the catalytically active surface.

The present types of catalysts are particularly efiective in removinghydrogen from chain compounds in such a way that cyclization may bepromoted without removal of hydrogen from end.

carbon atoms so that both end and side alkyl groups may appear assubstituents in benzene rings and it has been found that under properoperating conditions they do not tend to promote any great amount ofundesirable side reactions leading to the deposition of carbon orcarbonaceous'materials and for this reason show reactivity overrelatively long periods of time. When their activity begins to diminishafter a period of service, it is readily regenerated by the simpleexpedient of oxidizing with air or other oxidizing gas at a moderatelyelevated temperature, usually within the range employed in thedehydrogenation and cyclization reactions. This oxidation efiectivelyremoves traces of carbon deposits which contaminate the surface of theparticles and decrease their eificiency. It is characteristic of thepresent types of catalysts that they may be repeatedly regenerated withonlya very gradual loss of catalytic efficiency.

During oxidation with air or other oxidizing gas mixture in regeneratingpartly spent material, there is evidence to indicate that when the loweroxides are employed, they are to a large extent, if not completely,oxidized to higher .oxides' which combine with basic carriers to formcompounds of variable composition. Later these compounds are decomposedby contact with reducing gases in the first stages of service to reformthe lower oxides and regenerate the real catalyst and hence thecatalytic activity.

Erample I A n-hexane charge obtained by the careful fractionation of aPennsylvania crude oil was found to have a boiling point of 68.8 C. anda refractive index of 1.3768 which corresponds closely to the propertiesof the pure compound. This material was vaporized and passed over agranular catalyst comprising an alumina base supporting a minorproportion by weight of vanadium sesquioxide.

The catalyst was prepared by, dissolving 15.4-

200 parts by weight of hot water and adding the solution in twoequalsuccessive portions to 250 parts by weight of a 10-12'mesh activatedalumina. After the addition of the first half of the solution theparticleswere somewhatdamp and were dried at a steam temperature toremove excess water. After the heating the second half of the solutionwas added and the dehydration repeated. During the heating periodammonia and water were evolved leaving vanadium pentoxide deposited onthe alumina particles.

The final steps in the preparation of the catalyst comprised heating atZOO-250 C. for several hours, adding the particles to a catalyst chamberin which they were brought up. to the necessary reaction temperature inacurrent of air, and then subjecting them to the action of hydrogen atthe operating temperature to produce the lower oxides, this change beingaccompanied by a Example II n-Heptane was treated with the same type ofcatalyst as in-Example I at a'temperature of 550 C.,-substantiallyatmospheric pressure and 10 secs. contact time, The yield of toluene ona oncethrough basis was found to be 48% by weight and again it was foundthat by recycling the unconverted neheptane that the yieldof the desiredtoluene could ultimately be brought to 79%. v

, Ezrample III The general procedure in the manufacture of the catalystwas to dissolve the mixed fluoride of potassium and columbium in waterand utilize thissolution as a means of adding columbium compounds to acarrier. A saturated solution of this salt was made up in about parts ofwater and this solution was then added to about 250 parts by weight ofactivated alumina which had been produced bycalcining bauxite at atemperature of about 100 C. followed by grinding and sizing to produceparticles of approximately 8-12 mesh. Using the proportions stated thealumina exactly absorbed the solution and the particles were firstdriedat 100 C. for about 2 hours and the temperature was then raised to 350C. in a period of 8 hours. After this calcining treatment the particleswere placed'in a reactionchamber and the residual compounds heated in acurrent "of hydrogen at about 500 C., when they were then ready forservice.

n-Hexane was vaporized and passed over the granular catalyst, using atemperature of 515 C., substantially atmospheric pressure, and a time ofcontact of 18 secs. The yield of pure benzene under these conditions wasfoundto be 46% by weight of the normal n-hexane charged. By reycling ofthe unconverted material the ultimate yield of benzene was raised to76%. 3

Example IV n-Heptane was treated with the same type of catalyst as inExample III at a temperature of 56 C., substantially atmosphericpressure and sired toluene could ultimately be brought to 76%.

Example V Owing to the relative insolubility of most of the compounds oftantalum the method of dry mechanical mixing-was resorted to in. makingup a catalyst. Thus one part by weight of tantalum dioxide was mixedwith about 10 parts by weight of activated alumina which had beenproduced by calcining bauxite at a temperature of about 700 0., followedby grinding andsizing to produce particles of approximately 8-12 mesh.-The catalyst particles were not treated with hydrogen on account of theknown difllculty in reducing tantalum oxide although some reductionevidently took place when the hydrocarbon gas was passed over the massin the first stages of the treatment.

The n-hexane described above was vaporized and passed over a granularcatalyst comprising the alumina base supporting about 4% by. weight oftantalum sesquioxide, using a temperature of 520 C., substantiallyatmospheric pressure, and a time of contact of 19-secs. The yield ofpure benzene under these conditions was found to be by weight of thenormal n-hexane charged. By recycling of the unconverted material theultimate yield of benzene was raised to 75%,

Example Vi n-Heptane was treated with the same type of catalyst as inExample V at a temperature of 565 0., substantially atmospheric-pressureand 14 secs. contact time. The yield of toluene on a once-through basiswas found to be 45% by weight and again it was found that by recyclingthe unconverted n-heptane that .the yield of the' desired toluene couldultimately be brought to I Example VII To illustrate the resultsobtainable in the di rest dehydrogenationand cyclization of olefinsusing catalysts according to the present invention, the conversion ofl-hexene into benzol using a vanadium oxide on alumina catalyst preparedgenerally in accordance with the method given in Example'I may be cited.The vapors of the n-hexene were passed over the catalyst at atemperature of approximately'510" C. at atmospheric pressure at a ratecorresponding to a total contact time of approximately 20' seconds,which produced a once-through yield of 72% benzol which could be raisedto about by recycling oi unconverted olefln.

: Example VIII As a further example of the applicability of the presenttypes of catalysts andthe preferredoxides on alumina and was prepared ingeneral I accordance with the procedure outlined in Example III. At;atemperature of 505 C. substantially atmospheric pressure and a time ofcontact of about 18 seconds, there was produced a yield of tolueneequalin weight to almut 74% of the n-heptene charged. Recycling againincreased the overall yield to 90%.

We claim as our invention:

1. A process 'for the production of aromatic" hydrocarbons fromvaliphatic hydrocarbons of from six to twelve carbon atoms, whichcomprises ,dehydrogenating and cyclicizing the allphatic hydrocarbon bysubjection to a temperature ofrthe order of 400 to 700 C. for a-periodof about 6 to 50 seconds, in the presence of a compound of a metal fromthe left hand column of Group V of the periodic table and selected fromthe class consisting of vanadium, columbium and tantalum.

2'. Aprocess for the production of aromatic hydrocarbons from aliphatichydrocarbons --of from six to twelve carbon atoms, which comprisesdehydrogenating and cyclicizing the allphatic hydrocarbon'by subjectionto a temperature of the order 'of 400 to 700 C. for a period of about 6to 50 seconds, in the presence of 'an oxide of a metal from the lefthand column of Group V of the periodic table and selected from the classconsisting of vanadium, columbium and.-

tantalum.

3. A process for the production of aromatic hydrocarbons from aliphatichydrocarbons of from six to twelve carbon atoms, which comprisesdehydrogenating and cyclicizing the allphatic hydrocarbon by subjectionto a temperature of the order of 400 to 700 C. for a period of about 6to 50 seconds, in the presence of a .solid'granular catalyst comprisingessentially a major proportion of a carrier of relatively low catalyticactivity supporting a minor proportion of a compound of a, metal fromthe left hand column-oi Group V of the 'Deriodietable and selected fromthe classconsisting of vanadium, columbium and tantalum.

4. A process forthe production of aromatic hydrocarbons from aliphatichydrocarbons of from six to twelve carbon atoms, which comprisesdehydrogenatingand cyclicizing the allphatic hydrocarbon by subjectionto a temperature of the order of 400 to- 700 C. for a period of about 6to 50 seconds, in the .presence of a solid granular catalyst comprisingessentially a major proportion of -a carrier of relatively low catalyticactivity supporting a minor proportion of an oxide of a metal from theleft hand column of Group V of the periodic table and selected from theclass consisting of vanadium, columbium and tantalum.

- JACQUE C. MORREIL.

ARIS'I'ID V. GROSSE.

